1. Field of the Invention
The invention relates to a method and a device for fixing a connector on a printed circuit board, which connector is provided with fixing pins which are inserted into corresponding holes in the board, and are then heated and upset by means of a press tool at the side of the board facing away from the connector, in order to form a fixing head.
2. Description of Related Art
Methods are generally known, in particular, for fixing connectors which permit a modular construction. This means that these connectors can be fitted next to one another without loss of position. In the case of such connectors no fixing devices can be used at the ends, so that one has to resort to fixing devices situated at the rear side of the board.
According to a known method, the fixing pins are heated by means of the press tool, which is brought to the desired temperature beforehand. Pressing the press tool in a suitable manner causes part of the pin projecting through the board to be reshaped to a head, as a result of which a sort of rivet is formed.
This known method has various disadvantages. In order to obtain a sturdy fixing of the connector on the board, the connector must be pressed hard until the head formed has cooled off and is strong enough. For this purpose the connector is held pressed between a supporting face and the above-mentioned press tool. This pressing action is not, however, achieved until after the head is already formed. Only when the press tool has reshaped the pin in such a way that a head is obtained can the board be pressed against the appropriate face of the connector.
This means that the board cannot be kept pressed constantly against the connector during the formation of the head. During the initial deformation of the pin the board lies, as it were, still loose against the connector, which can lead to undesirable movements and thereby a poor fixing. Finally, the press tool must be held against the head until the latter has cooled off sufficiently, something which can take some time, since the head itself also has a certain heat capacity
Another disadvantage lies in the fact that the thickness of the board can vary within certain tolerances. This has a direct influence on the length of the pin part to be deformed, and thus on the volume to be reshaped. Since also the material is not impeded in the lateral direction during reshaping, in the case of a relatively thin board, and thus in the case of a relatively large volume of the pin to be reshaped, this pin material can give way laterally under the press tool. A thin, irregularly shaped edge all the way around the deformed head is consequently obtained. Apart from the fact that such an edge is not visually acceptable, it also produces the risk of polluting soldering bath through which it must be possible to pass the board with the connector. Besides, plastic particles can come off as a result.
It is also found in practice that during the heating and reshaping the pins can be pressed into a crooked position, which is also a disadvantage for the strength of the connection obtained. This also makes it difficult to hold board and connector pressed well against each other.
The boards on which the connector has to be fixed can be supplied in various standard thicknesses, for example, 1.6 and 2.4 mm. Since, as described above, the press tool according to the state of the art can function properly only if the pin is of a certain length, this means that for boards of a different thickness connectors with differing pin lengths have to be used. This is undesirable, in view of the additional costs which keeping two different types of connector in stock involves. All this could be allowed for by adapting the press tool, but the disadvantage of this is that it would have to be changed constantly.
The final disadvantage which will be mentioned is that through contact with the hot press tool the plastic material of the pins could stick, which soils the press tool and give the fixing head obtained a ragged appearance.